1. Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of improved contact hole creation for ultra-small contact holes.
2. Description of the Prior Art
Integrated semiconductor devices comprise electronic circuits of sub-micron and deep sub-micron dimensions and are typically created in or on the surface of a silicon substrate. The creation of semiconductor devices is supported by sophisticated and interacting, mutually supporting disciplines.
Device features are transposed from a mask onto a semiconductor surface using photolithographic imaging processes. Since this exposure depends on the transfer of photo energy from a source to a target surface, it is to be expected that, for target features that are created in very close proximity to each other, the transfer of photo energy interacts for very closely spaced device features, most commonly interconnect lines or contact holes having sub-micron spacing between adjacent lines.
A common measure for the occurrence of such interactions are applications where the Critical Dimensions (CD) of the layout of the Integrated Circuit (IC) approach the resolution limit of the lithography equipment. For such applications, proximity effects begin to influence the manner in which mask images are transferred to target surfaces. This interaction imposes limitations on the proximity of adjacent device features; these limitations are referred to as Critical Dimensions (CD) of a design and device layout.
The invention addresses problems and limitations that are encountered when creating openings on a semiconductor surface such as the surface of a layer of photoresist or the surface of a semiconductor substrate.
U.S. Pat. No. 5,573,634 (Ham) shows a double exposure contact hole method.
U.S. Pat. No. 6,218,057 (Cirelli et al.) shows a lithographic process for contact holes using 2 masks/exposures.
U.S. Pat. No. 6,238,850 (Bula et al.) shows a photo method for contact holes using 2 masks/exposures.
U.S. Pat. No. 5,308,741 (Kemp), U.S. Pat. No. 5,897,975 (Ahn et al.) and U.S. Pat. No. 5,795,686 (Takizawa et al.) are related photo methods.